1. Field of the Invention
The invention relates to a process for the treatment of hydrocarbon-containing waste material, in particular plastic-containing waste material, which includes subjecting the waste material to pyrolysis with the addition of an additive material that binds acidic pollutants, feeding pyrolysis gas which is formed to at least one first precooling stage, and cooling the gas to a temperature below the condensation temperature of water vapor with the production of low-boiling pyrolysis oil in at least one second cooling stage downstream of the gas side the first precooling stage.
2. Description of the Related Art
The pyrolysis gas formed in the pyrolysis of hydrocarbon-containing waste material, in particular plastic wastes, contains hydrocarbons and, depending on the nature and composition of the waste material, more or less water vapor and a number of gaseous pollutants, namely: compounds of nitrogen, chlorine, sulphur and fluorine, and cyano compounds. Of these pollutants, especially the halogens chlorine and fluorine are extremely aggressive, so that metal parts subjected to the pyrolysis gases must be of a particularly corrosion-resistant and therefore expensive construction. In the cooling stages, where low-boiling pyrolysis oil is obtained by cooling of the pyrolysis gas to a temperature below the condensation temperature of water vapor, in most cases to 30 to 80.degree. Celsius, under approximately ambient pressure, the water formed from the water vapor of the pyrolysis gas absorbs the above-mentioned pollutants, and in particular the halogens fluorine and chlorine in the form of their hydrogen compounds. As a result of this loading with pollutants, the water assumes the properties of an acid, so that the components coming into contact with this water must also be acid-resistant and are therefore correspondingly expensive. Furthermore, the disposal of this pollutant-laden water entails additional costs.
In order to reduce the formation of pollutants, it is therefore usual to introduce a basic, fine-grained additive material, preferably calcium carbonate, hydrated lime, calcium oxide, magnesium carbonate, magnesium oxide, dolomite or sodium hydroxide, as an individual material or as any desired mixture of these individual materials, into the pyrolysis reactor during the pyrolysis process, that is to say to carry out the pyrolysis in the presence of these materials. As a result, the acidic pollutants are largely, and in the limiting case completely, bound immediately after their formation by the basic additive material, so that the aggressiveness of the pyrolysis gas and of the water arising is eliminated or, on the other hand, at least considerably reduced In this case, the pH value is in the region around the value 7 and, exactly 7 in the ideal case.
The additive material in most cases is added in a more than stoichiometric ratio, relative to the waste material, that is to say more additive material is added than is theoretically required for binding the pollutants. This is necessary for reliable binding of these pollutants. The quantity of additive material required for binding the pollutants, depends on the composition of the waste material and is determined by calculation based on the constituents of the waste material, or experimentally. Since the composition of the waste material then frequently changes and/or the pyrolysis conditions, such as the pyrolysis temperature and the mixing of the waste material with the additive material, do not remain constant, especially in long-term operation, it is desirable to detect such changes, so that the addition of the additive material can be adjusted correspondingly. Since the additive material after the reaction increases the quantity of pyrolysis residue, which in most cases cannot be utilized, it is also for this reason that monitoring of the addition of the additive material is necessary, in order to avoid unnecessary over-additions.